1. Field of the Invention
The present invention relates to the a structure of films above photodiodes of a solid state camera element.
2. Description of the Related Art
Hitherto, as shown in Japanese Patent Laid-open No. 326763/1992 publication, a fluorescence film is used above a photodiode of a solid state camera element to increase blue sensitivity. FIG. 1 illustrates the structure of a photodiode of a solid state camera element shown in the Japanese Patent Laid-open No. 326763/1992. In this example of the prior art, a photodiode 27 is provided on silicon substrate 26, and protection film 28 and fluorescence film 29 are formed on the photodiode 27, successively. The fluorescence film 29 has an absorption area in a desired wavelength zone of which sensitivity improvement is intended, and hence it emits light on the longer wavelength side of the desired wavelength zone, the longer wavelength side corresponding to the high sensitivity wavelength of photodiode 27. Since there are large differences in refractive index between the silicon substrate 26 on which the photodiode is formed and the silicon oxide film interface, and blue sensitivity is largely lowered due to the reflection and scattering of light in the interfaces, light is converted to light having longer wavelength by means of fluorescent pigment before the blue light is damped in the interfaces between the silicon substrate and the oxide film to improve blue sensitivity. Also in a solid state camera element, into which signals are inputted from the rear side, blue color is largely damped when it is inputted into the substrate on which sensors are formed, and hence blue sensitivity is improved by providing a fluorescence film on the rear side.
Also, as shown in Japanese Patent Laid-open No. 322467/1992, in the case that there is shown in FIG. 2 a solid state camera element in which microlens 33 is formed in the upper part of the element as shown in FIG. 1 to collect signals on a photodiode 31, fluorescent pigment is mixed into a microlens 33 and further a layer of fluorescence reflection film 34 is formed on the fluorescence film 33. The fluorescence reflection film 34 reflects luminescence wavelength light of microlens 33, and it enables the fluorescence, which does not enter photodiode 31, to enter photodiode 31, efficiently.
In the structure illustrated in FIG. 1, as shown in Japanese Patent Laid-open 326763/1992, since fluorescence is emitted in all directions, fluorescence emitted in a direction, in which it is not allowed to be applied to photodiode 27 becomes a loss and also when it enters the adjacent photodiode, it becomes an error signal so that the resolution is deteriorated.
Further, when fluorescence pigment is mixed with microlens 33 as illustrated in FIG. 2, and in Japanese Patent Laid-open 322467/1992, distribution of the refractive index becomes irregular because of the uneven density of fluorescence pigment in microlens 33, resulting in the lowered efficiency in condensing light to photodiode 31. One layer of fluorescence reflection film 34 also can not produce large effects.
Further, if the reflected light from fluorescence reflection film 34 enters a neighboring photodiode, it produces an error signal, deteriorating the resolution of images.